1. Field of the Invention
This invention relates to a catalyst composition and methods for making the catalyst which is capable of sustained high temperature operation.
2. Description of the Previously Published Art
Catalysts to carry out combustion of crude oil, hydrocarbon fuels, coal derived fuels, coal slurries as well as hydrogen are being made with the objectives of maximizing the heat output of the fuel as well as minimizing carbon monoxide, hydrocarbon and nitrogen oxide emissions. Reducing combustion temperatures to 1500.degree. C. and below result in reduced nitrogen oxide emissions since the N.sub.2 +O.sub.2 .fwdarw.2NO reaction is not favorable below that temperature. However, reducing the combustion temperatures by non-catalytic means still presents problems. If the amount of air is decreased to provide rich conditions, then there will be increased emissions of CO and hydrocarbons. If the amount of air is increased to provide lean conditions, then there will be increased NO.sub.x emissions as well as inefficient combustion as much of the heat generated during combustion is consumed in heating the diluent gases.
Catalytic combustion has the advantages of simultaneously reducing emission levels of all three components while efficiently combusting the fuel. It also has the advantage of permitting nearly complete combustion closer to the stoichiometric oxygen level. Because operation must be sustained at very high temperatures i.e., about 1200.degree.-1300.degree. C., for efficient operation, there is a need for ultra stable catalysts. Noble metals are effective catalytic components that have been used in first generation combustor systems. Many of the catalysts are auto exhaust type catalysts which are not designed for very high temperature operation. The Ernest et al U.S. Pat. No. 4,170,573 discloses a catalyst composition comprising a composite of ceria, lanthana, and alumina with a catalytically-effective amount of one or more platinum group metals. At higher temperatures, however, noble metals exhibit increased vapor pressure in air and can result in significant losses of noble metals. For that reason a totally noble metal type system is not seen as a viable candidate for sustained ultra high temperature operation.
Base metal oxides (such as Cr.sub.2 O.sub.3) having low vapor pressure would be preferred. However, because of their dense, highly crystalline nature, they inherently do not bond well to ceramic substrates. Good bonding is a necessity due to the very high flow velocities encountered in combustor systems.
3. Objects of the Invention
It is an object of this invention to produce a catalytic composition which is capable of sustained operation at very high temperature and which will efficiently combust fuel with minimum oxygen present.
It is a further object of this invention to produce a catalytic composition which when used in catalytic combustion will result in low emission levels.
It is a further object of this invention to produce a washcoat composition which can be applied to a substrate to form an efficient combustion catalyst that operates at high temperatures.
It is a further object of this invention to provide a method of forming a washcoat composition which after application to a substrate will firmly bond to the substrate and operate efficiently.
These and further objects will become apparent as the description of the invention proceeds.